1. Field of the Invention
The present invention relates in general to automatic transmissions for wheeled motor vehicles, and more particularly a speed change mechanism of the automatic transmissions, which comprises two planetary gear units which are coaxially arranged, two clutches which are arranged to selectively transmit a speed-changed input rotation to rotational elements of the mechanism and brakes which are arranged to selectively fix other rotational elements of the mechanism for allowing the transmission to assume a desired speed or position.
2. Field of the Related Art
Nowadays, for improving fuel consumption and drivability of the motor vehicles, the speed change mechanisms of automatic transmissions have a tendency to increase the number of speeds, viz., speed positions. One of them is shown in Laid-open Japanese Patent Application (Tokkai) 2000-55152, which comprises a planetary gear unit that mainly reduces the speed of rotation transmitted from the engine, a speed change mechanism that is arranged behind the planetary gear unit, two direct clutches that are capable of directly transmitting the rotation of the engine to rotational elements of the speed change mechanism and brakes that are capable of fixing the rotational elements of the speed change mechanism, for allowing the transmission to have a plurality of speeds.
The speed change mechanism of the above-mentioned application employs a Ravigneawx type planetary gear unit. That is, by selectively engaging or disengaging the clutches and brakes in a controlled manner, the rotational elements of the speed change mechanism are arranged to constitute a power transmitting path for a desired speed.
However, due to its inherent construction, usage of the Ravigneawx type planetary gear unit as the speed change mechanism causes the mechanism to have a bulky construction, that is, a bulky construction whose size is enlarged in a radial direction. That is, for transmitting the speed reduced input rotation (viz., speed changed rotation) from the speed reducing planetary gear unit to the two sun gears of the Ravigneawx type planetary gear unit through the above-mentioned two clutches, there is a need of providing two connecting members, one being for connecting one of the clutches to one of the sun gears and the other being for connecting the other clutch to the other sun gear. However, due to inevitability in layout, the two connecting members are compelled to have axially extending portions which are concentrically overlapped on each other, which causes enlargement of the speed change mechanism in a radial direction.